Another P0300

[intergalactron]

I have a 2020 Tahoe LT, 5.3 Flexfuel, 110,000 miles. It has a stored P0300 code. This code was set during a hard acceleration event (merging on an on ramp). Engine backfired, lost power, engine light came on and was flashing. I let off the gas and everything returned to normal. Engine light turned off within a few seconds. This has happened 3 or 4 times. All similar circumstances, but only the one time I noticed the engine light coming on/flashing.

Other possibly related symptoms: Occasional rough idle. Occasional poor shift quality. Occasional 'surging' (throttle held steady, engine rpm varying).

I'm at the beginning of trying to get this ironed out. Where do you suppose I ought to start looking?

 

[Geotrash]

I have a 2020 Tahoe LT, 5.3 Flexfuel, 110,000 miles. It has a stored P0300 code. This code was set during a hard acceleration event (merging on an on ramp). Engine backfired, lost power, engine light came on and was flashing. I let off the gas and everything returned to normal. Engine light turned off within a few seconds. This has happened 3 or 4 times. All similar circumstances, but only the one time I noticed the engine light coming on/flashing.

Other possibly related symptoms: Occasional rough idle. Occasional poor shift quality. Occasional 'surging' (throttle held steady, engine rpm varying).

I'm at the beginning of trying to get this ironed out. Where do you suppose I ought to start looking?

Fuel pressures.

 

[intergalactron]

Fuel pressure: 40-50 psi
Fuel rails: 450-600 psi

 

[intergalactron]

I did check my MAF sensor, didn’t see any dust or buildup on it. I hit it with a little canned air just to be sure it was clean, put it back, still runs the same.

 

[OR VietVet]

There is MAF cleaner to buy at the parts store. Better than air attempt.

 

[NardDog]

I did check my MAF sensor, didn’t see any dust or buildup on it. I hit it with a little canned air just to be sure it was clean, put it back, still runs the same.

Try unplugging it and see it runs better

 

[intergalactron]

Try unplugging it and see it runs better

That's a good idea. I had a Buick that had the MAF completely fail. Wouldn't run. Unplugged it and it went into a 'safe' engine map and ran fine.

 

[Fless]

At warm idle, what does your scanner say the MAF reading is in g/s? It should be very close to the engine displacement in liters (or "litres" if you go that way...)

 

[intergalactron]

So its cold and snowy where I live so I've kinda back-burnered this. But I was thinking... My driver's side motor mount is shot. Could a little bit of clunking of that motor mount trip the knock sensor, causing some of this surging?

 

[OR VietVet]

So its cold and snowy where I live so I've kinda back-burnered this. But I was thinking... My driver's side motor mount is shot. Could a little bit of clunking of that motor mount trip the knock sensor, causing some of this surging?

Yes. Knock sensors react to noise.

 

[intergalactron]

Replaced the drivers side engine mount over the weekend. This is the process I used:

A couple of notes from my experience:
1. Take out the steering shaft, just gives you more room to work.
2. Go ahead and cut off the heat shield on the old mount. Again, more room to work, particularly on the 4 bolts that hold the mount to the motor.

Best tip in the video is to remove the heat shield on the new mount and tap the rivet holes (or use sheet metal screws) and put the heat shield on after getting the mount in place.

The new mount definitely cleaned up the shifts. It really liked to stumble immediately after shifting before.

 

[intergalactron]

After driving it for a couple of weeks now, changing the motor mount fixed most of my problems. Forced to conclude that it was probably the knock sensor picking up noise from the clunking motor mount.

Doesn't tell me why I got the P0300 code, I don't think. I did get the even more dreaded P06DD code the other day. It never ran poorly and cleared on it's own. Maybe the two are related...

 

[intergalactron]

Wow did I ever jinx myself... Wife took the truck to get groceries, calls me, says it's missing. Throwing P0324 (knock sensor) and P0307 (#7 Misfire). After swapping coils around to see if that was the issue, the P0307 code changed to P0300. Did a compression check on #7. No compression. Tore it down on the driver's side, found the #7 intake lifter stuck in the bore. And I mean stuck. Won't budge.

Just crazy. Went from running great to in need of serious work in the space of 5 seconds. This is a motor, despite having almost 120K miles on it, that didn't even hardly get the oil dirty after 5k miles... I'm just beside myself.

 

[Geotrash]

Wow did I ever jinx myself... Wife took the truck to get groceries, calls me, says it's missing. Throwing P0324 (knock sensor) and P0307 (#7 Misfire). After swapping coils around to see if that was the issue, the P0307 code changed to P0300. Did a compression check on #7. No compression. Tore it down on the driver's side, found the #7 intake lifter stuck in the bore. And I mean stuck. Won't budge.

Just crazy. Went from running great to in need of serious work in the space of 5 seconds. This is a motor, despite having almost 120K miles on it, that didn't even hardly get the oil dirty after 5k miles... I'm just beside myself.

This sucks, man. I'm sorry.

I responded to your question on the new thread but will share here also for the listening audience. If that lifter is really stuck in there, the motor may need to come out and taken to a machine shop to get the thing out and the lifter bore sleeved. If you can get the cam out, you might be able to drive it out from the top. The only other ting I could suggest is to drill a hole into the top of the lifter and put a self tapping screw or eyelet in there. You might be able to get a small slide hammer on it that way to drive it upwards.

 

[OR VietVet]

That engine is jinxed. IMO, get another or a whole other truck. Jinxed is jinxed.

Man, I love my GMT800 more and more every day.